1. Field of the Invention
This invention relates generally to a method and mold for producing round metallic stock, and more specifically to a method and mold for producing round rods for use as consumable welding electrodes from an uncompacted particle mass.
2. Description of the Prior Art
Generally speaking, consumable welding electrodes of low-alloy carbon steel composition are obtained from rod stock that has received a coating of flux. Such stock is produced by casting a melt, forming billets and hot rolling the billets on a rod mill into rods. Depending upon the desired electrode diameter the rod may be used in this form or converted to smaller diameters in any conventional manner. This process is suitable for economically producing large quantities of such electrodes for welding low-alloy carbon steel stock. Many product forms, however, are fabricated from stainless steels, super alloys and cast irons. To weld these products high alloy and cast-iron electrodes are required.
Some alloy and cast-iron welding electrodes can be obtained from rods produced by casting into sand mold cavities. Typically a melt of a specific composition is prepared and poured into a mold. Although this technique can produce generally satisfactory electrodes in diameters larger than 1/2 in. the process has several deficiencies.
The process is expensive because sand molds can only be used once; rod size is limited by casting; gates and risers generate scrap; and compositions amenable to casting are limited. Furthermore, a portion of the mold sand usually adheres to the cast product requiring some reconditioning by grinding.
Alloy and cast-iron welding electrodes are also produced by chill molding wherein permanent molds obtained from rods are employed. Although contamination of the cast product has been eliminated this technique is limited by the compositions which can be conveniently and economically cast.
In the past welding electrodes have also been manufactured through the use of powder metallurgy. One such technique is disclosed in U.S. Pat. No. 3,650,736 wherein powders are mixed together with a binder and compacted in a mold under pressure. The compact is thereafter sintered at an elevated temperature. This process requires the use of non-contaminating, expendable binders and compaction prior to sintering.
In my U.S. Pat. No. 3,860,420 filed June 18, 1973 I disclose a powder metallurgy method for manufacturing rods for welding electrodes without employing compaction or binding agents. A particle mass is poured into a mold cavity and heated in a protective atmosphere according to a predetermined heating schedule. As used herein particle mass is defined as a single pre-alloy powder or combination of powders formulated to yield metallic stock of a specific alloy composition, homogeneity level and purity level.
Although the process disclosed in this patent produces satisfactory rods from a metallurgical standpoint, that is, uniformity of composition and structure the rod cross-section, for some applications is objectionable, in that it is not round. Round rods for welding electrodes are desirable because they can be easily coated with welding fluxes and furthermore proper electrical contact is insured when they are clamped into a welding power source.
The present invention produces substantially round rods for welding electrodes by powder metallurgy without the employment of binders or compaction prior to sintering.